Sample receiving mechanism

ABSTRACT

A tiltable tray mechanism is provided having a fixed support member, a normally horizontally disposed tray arranged above the support member, a piston and cylinder assembly fixedly mounted to the support member and disposed beneath the tray, and a clevis and pin arrangement for connecting the piston to the tray so that the tray is tiltable with respect to the piston out of its normally horizontal position. The piston and cylinder assembly has its piston generally vertically disposed and extending toward the tray. A coil spring is interposed between the tray and the fixed support member for urging the tray into the normally horizontal position, and the piston is operable upon retraction into its cylinder to overcome the bias of the spring and tilt the tray. A stop carried by the fixed support member is laterally displaced from the vertically disposed piston, the stop being located beneath the tray for engagement by the tray in response to retraction of the piston into its cylinder so that such engagement causes the tray to be tilted with respect to the horixontal and against the bias of the spring. A guide pin is fixed to the underside of the tray and extends through an opening provided in the fixed support member for engagement with the sides of the opening to thereby limit the extent of tilting movement of the tray.

United States Patent 1 Smith SAMPLE RECEIVING MECHANISM [73] Assignee: Packard Instrument Company, Inc.,

Downers Grove, lll. W

[22] Filed: Apr. 10, 1972 [21] Appl. No.: 242,443

[52] U.S. Cl 141/272, 53/368, 141/88,

211/81 [51] Int. Cl. 1365b 3/04 [58] Field of Search 53/368; 211/81, 168;

[56] References Cited UNITED STATES PATENTS 3,301,281 1/1967 Lau 141/272 Primary Examiner-Houston S. Bell, Jr. Assistant ExaminerFrederick R. Schmidt AttorneyC. Frederick Leydig et al.

[57] ABSTRACT A tiltable tray mechanism is provided having a fixed 1 Nov. 27, 1973 support member, a normally horizontally disposed tray arranged above the support member, a piston and cylinder assembly fixedly mounted to the support member and disposed beneath the tray, and a clevis and pin arrangement for connecting the piston to the tray so that the tray is tiltable with respect to the piston out I of its normally horizontal position. The-piston and cylinder assembly has its piston generally vertically disposed and extending toward the tray. A coil spring is interposed between the tray and the fixed support member for urging the tray into the normally horizontal position, and the piston is operable upon retraction into its cylinder to overcome the bias of the spring and V tilt the tray. A stop carried by the fixed support member is laterally displaced from the vertically disposed piston, the stop being located beneath the tray for engagement by the tray in response to retraction of the piston into its cylinder so that such engagement causes the tray t o hgtilted with esgegt to the horizontal and against the bias of the spring. A guide pin is fixed to the underside of the tray and extends through an opening provided in the fixed support member for engagement with the sides of the opening to thereby limit the extent of tilting movement of the tray.

6 Claims, 4 Drawing Figures 1 SAMPLE RECEIVING MECHANISM DESCRIPTION OF THE INVENTION The present invention relates generally to a mechanism for receiving and collecting fluid samples to be subjected to later tests or determinations. More particularly, the invention relates to a mechanism for receiving fluid samples for radioactive isotope tracer studies.

Various techniques have been devised for the preparation of samples for radioactive isotope tracer studies. A particularly efficient and commercially attractive technique for such sample preparation involves combustion of a starting material containing one or more isotope tracers, recovery and liquefaction of the gaseous combustion products containing the isotopes, and isolation of the individual isotopes to permit their quantitative determination.

A combustion technique of this type (combustionrecovery-isolation) has been disclosed in pending Kaartinen application Ser. No. 277,261 filed Aug. 2, 1972. That technique involves placement by an operator or technician of an isotope tracer containing material into an apparatus for combustion, followed by automatic starting, controlling and termination of various flows of gases and liquids used in preparing the samples. The resulting liquid samples are deposited in sample receiving vials suitable for removal from the apparatus and relocation in scintillation counting equipment where the sample radioactivity is quantitatively determined. Following preparation of the liquid samples, the sample preparation apparatus described in the aforementioned Kaartinen application includes provision for thoroughly cleaning the apparatus to remove any residual traces of radioactivity therein so as not to contaminate subsequently prepared samples.

It is a primary object of the present invention to provide an improved sample receiving mechanism for use in an apparatus for the preparation of samples for radioactive isotope tracer studies. A related object is to provide such a mechanism which receives and collects samples in sample vials normally mounted at outlets provided in the apparatus, but which is capable of shifting the sample vials away from the apparatus outlets during cleaning of the apparatus and substituting a waste receiving container for the vials.

Another important object of the present invention is to provide an improved sample receiving mechanism which is compact, has few moving parts, and is designed and constructed to be easily automated, e.g., in response to a programmed control unit.

Other objects and advantages of the invention will become apparent from the following detailed description and upon reference to the accompanying drawings, in which:

FIG. 1 is a side elevational view of an illustrative sample receiving mechanism embodying the present invention showing the sample vials in sealed (solid lines) and unsealed positions (dotted lines) with respect to a sample preparation apparatus:

FIG. 2 is a side elevational view of the illustrative sample receiving mechanism similar to FIG. 1 but showing the mechanism in a tilted condition for receiving waste liquids.

FIG. 3 is a fragmentary front elevational view of the illustrative sample receiving mechanism shown in FIGS. 1 and 2; and

FIG. 4 is a top plan view of the sample receiving mechanism shown in FIGS. 1-3.

While the invention will be described in connection with certain preferred embodiments, it will be understood that it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims.

As indicated, the present invention is advantageously used in conjunction with an apparatus for the preparation of samples for radioactive isotope tracer studies, such as studies involving tissue distribution and residue levels of drugs in plants and animals. In the preparation of such samples, the starting material containing the radioactive isotope tracer, such as plant or animal tissue, is burned to convert the carbon in the starting material to carbon dioxide and the hydrogen to water, and the radioactive isotope tracer is then recovered from the resulting combustion products. For example, if the particular radioactive isotope tracer employed is C, it appears in the combustion products as CO gas; if the tracer is tritium (I-I), it appears in the combustion products as H O in the form of a condensable vapor. Although C and H are the most commonly employed tracers, it will be understood that a number of other radioactive isotopes may be employed, such as S which is converted to sulfate during combustion.

In order to provide samples which can be analyzed for radioactivity, the compounds containing the isotope tracers are recovered from the combustion products, and separated from any materials therein which might interfere with the radioactivity determination. For example, the I-I O is recovered by cooling the combustion products to condense the vapors therein, including the H 0, after which the condensed vapors are separated from the remaining gases. The CO may also be recovered by condensation or freezing at extremely low temperatures, such as by the use of liquid nitrogen for example, but it is more conventional to react the CO with a liquid trapping agent such as a particular amine compound; the resulting reaction product is then recovered and mixed with a liquid scintillator to provide a sample suitable for use in making a radioactivity determination.

As described in the aforementioned Kaartinen application, the sample preparation apparatus (not shown generally in the drawings) includes a combustion chamber followed by various units, interconnecting conduits, and associated apparatus for treating the gaseous combustion products to separate and effect recovery of each radioactive isotope tracer. The apparatus in this instance is particularly adapted for recovery of H and C isotope tracers.

The overall operation may be described generally as follows. Material containing the radioactive isotope tracers is placed in an ignition basket within the combustion chamber. The apparatus operator thereupon pushes a start button for a pre-programmed pneumatic control unit, and combustion oxygen is admitted to the chamber. The isotope containing material is quickly ignited, and the resulting gaseous combustion products pass upwardly through the combustion chamber and then into a heat exchanger, for example a vertically oriented, air-cooled condenser. Water, including tritiated water, condensed from the combustion gases then passes through a heat exchanger outlet conduit 10, shown in the drawings, and collects in a tritium sample collection vial 11 located (in raised, sealed vial position FIG. 1) beneath the outlet 10.

Uncondensed gases exiting from the heat exchanger pass into and out of the headspace of the vial 11, and then continue into a primary tritium exchange column where exchange takes place between the tritiated water in the combustion gases and residual distilled water held in the column from the end of the previous cycle of the apparatus. The effluent gases from the primary exchange column continue on and enter a secondary tritium exchange column where further exchange takes place between any relatively tritium rich gases leaving the primary column and any entrained relatively tritium poor aqueous liquids carried into the secondary column from the primary column. The resulting exchanged tritiated water remains for the most part in the two exchange columns until the later flushing and cleaning steps (see below). At that time the tritiated water is flushed downwardly (by tritium scintillator solution) through the primary tritium exchange column and into the tritium collecting vial 11.

The uncondensed gases emerging from the secondary tritium exchange column then pass through a three-way valve and continue into a carbon sample collecting vial 12 disposed beneath the outlet 13 of a carbon reaction column. The reaction column contains a suitable carbon dioxide trapping agent, usually an amine compound, furnished from a suitable trapping agent supply.

As the gases enter the bottom of the reaction column, the carbon dioxide vapors move upwardly through the column and meet liquid trapping agent flowing downwardly. Heat is generated from the reaction between the carbon dioxide and the amine (some trapping agent becomes vaporized), and the intimate physical and chemical contact between gas and liquid results in fractional reaction taking place between the carbon dioxide and the trapping agent.

Any unreacted gases emerging from the reaction column (tend to be saturated with amine vapor) then pass into a carbon exchange column. From the end of the previous apparatus cycle the carbon exchange column contains residual carbon scintillator solution supplied from a suitable scintillator supply. In the carbon exchange column further fractional reaction and mixing takes place between any gaseous carbon dioxide present, the residual scintillator solution, and the trapping agent vapors.

The exit gases from the carbon exchange column, now thoroughly scrubbed of virtually all residual carbon dioxide but saturated with scintillator vapor, pass on through a second three-way valve and into a vented waste container. The waste container preferably contains a suitable liquid such as methanol through which the discharge gases are bubbled to scrub out any final residual carbon trapping agent or scintillator present, and the gases discharged to atmosphere are basically odor free.

Upon completion of combustion of the starting material, oxygen supply to the combustion chamber is terminated. Distilled water is then injected into the base of the combustion chamber, and approximately simultaneously an inert gas, such as nitrogen, is also admitted into the base of the combustion chamber. The water flashes to steam and the inert gas and water vapor sweep the products of combustion upwardly through the combustion chamber, through the heat exchanger outlet 10, and thence into the tritium sample collecting vial 11 where the condensed liquids are collected. Uncondensed gases leave the headspace of the vial l1 and continue on through the rest of the apparatus.

Now both of the three-way valves are shifted (preferably simultaneously) to isolate the carbon side from the tritium side of the apparatus, and to open both sides to access to inert gas (and water at the first valve). At the same time, the tritium sample receiving vial l1 and the carbon sample receiving vial 12 are partially lowered by means of a sample receiving mechanism 14 constructed in accordance with the invention (see dotted position in FIG. 1), as will be described in detail below, so that they are open to atmosphere, and feed of tritium and carbon liquid scintillator solutions to the apparatus is initiated.

Tritium scintillator solution is introduced between the primary and secondary tritium exchange columns, and carbon scintillator solution enters the carbon exchange column. Passage of the tritium scintillator solution downwardly through the primary tritium exchange column causes the exchanged liquid water within the column to be washed down through a return conduit 15 (from the primary tritium exchange column, shown in FIG. 3) and into the partially lowered tritium sample collection vial 11. On the carbon side, the carbon scintillator solution passes sequentially through the carbon exchange column and the carbon reaction column, with the resulting wash liquids flowing through the outlet 13 and into the partially lowered carbon sample collection vial 12.

Shortly after the start of tritium and carbon scintillator solution flow to the apparatus, a second inert gas sweep takes place. This time inert gas (preferably nitrogen gas) is admitted as before into the combustion chamber, and is also admitted through each of the three-way valves. The inert gas sweep through the combustion chamber forces residual gases and liquids therein through the heat exchanger outlet 10 and into the tritium sample collection vial 1 l. Purged liquids are retained in the via] 11; the gases are vented to atmosphere through the open vial mouth. Sweep gas admitted through the first three-way valve forces residual gases (but not liquids, except for any tritium scintillator solution which might have been introduced into the primary tritium exchange column in excess of its holding capacity) within the tritium exchange columns into the tritium sample collection vial 11. And the inert sweep gas entering the apparatus through the second threeway valve pushes gases within the carbon exchange column and carbon reaction column (as well as any liquids therein) downwardly through the outlet 13 and into the carbon sample collection vial 12. Once more, purged liquids are retained in the vial l2 and gases are vented to atmosphere through the open vial mouth.

A short time after commencement of the second inert gas flush, a mist cleaning cycle begins. This cleaning operation involves increasing all three of the inert gas flows (i.e., into the combustion chamber, and through the two three-way valves) to enhance the sweep forces available within the apparatus, and admission of distilled water to the combustion chamber and through the first three-way valve (along with the inert gases being fed at those locations). As described in detail below, the sample receiving mechanism 14 of the present invention is actuated to further lower and then tilt the tritium and carbon sample collection vials 11, 12 (see FIG. 2) so that their vial mouths are no longer accessible to fluids flowing downwardly through the outlets 10, (tritium) and 13 (carbon). In the tilted position of the sample receiving mechanism 14, fluids flowing from the outlets 10, 15 and 13 are diverted into a waste receiving compartment 16 in the mechanism 14.

The turbulent gas-liquid cleaning conditions thus created throughout the apparatus have been found to cleanse the apparatus of virtually all residual radioactivity in an extremely highly efiicient manner. The wash liquids which flow into the waste receiving compartment 16 of the mechanism 14 are then directed to a waste reservoir (not shown) via a conduit 18 and disposed of. The waste wash gases pass harmlessly into the atmosphere from the open compartment 16.

Following completion of the cleaning cycle, the two water and three inert gas feeds to the apparatus described above in connection with the cleaning cycle are terminated, the ignition basket is withdrawn from the combustion chamber in readiness for the next sample preparation, and the pneumatic control unit shuts off. Now the tritium sample collection vial 11 and carbon sample collection vial 12 may be removed from the sample receiving mechanism 14 by the apparatus operator, and the radioactivity of the tritium and carbon samples determined using a photomultiplier or other suitable radioactivity counting device.

In accordance with the invention, the sample receiving mechanism 14 includes a tiltable tray 19 for holding the sample receiving vials 11 and 12, a pneumatic piston and cylinder assembly 20 having the piston (not shown) arranged for vertical movement, and a link 21 integral with the piston and connected to the tray by means of a clevis 22 and pin 23 arrangement for trans mitting movement of the piston to the tray. The sample receiving mechanism 14 is mounted on a fixed lower support plate 24, to the underside of which the piston and cylinder assembly 20 is suitably attached.

The mechanism 14 is arranged within the sample preparation apparatus such that the sample vials l1 and 12 are normally aligned with and located directly beneath outlets l0 and 13 of the heat exchanger and carbon reaction column, respectively. Portions of the support structure for the heat exchanger and carbon reaction column are designated generally in the drawings as 25.

As shown in FIG. 4, the tray 19 is provided with front 26 and rear 16 compartments. The front compartment 26 is sized and shaped to hold both sample vials 11 and 12 in spaced apart, side-by-side relationship. The rear compartment 16, rectangular in cross-section, is adapted to receive various waste fluids from the apparatus (produced during cleaning) and transmit them through the conduit 18 into the waste reservoir (not shown).

The sample receiving mechanism 14 is constructed to support the tiltable tray 19 at one of three operating positions. These are (a) a sealed vial position, i.e. with the vials 11 and 12 sealed tightly against the support structure and thus against the outlets 10 and 13 of the heat exchanger and carbon reaction column, respectively, (b) a partially lowered position, i.e., with the vials 11 and 12 disengaged from the support 25 but still aligned directly beneath the outlets l0 and 13, respectively, and thereby open to the atmosphere while 6 still being positioned to collect liquids from these outlets, and (c) a tilted position in which the vials l1 and 12 are tilted away from the outlets 10 and 13, and instead the waste receiving compartment 16 is arrangedbeneath these outlets so that fluids from the heat exchanger and carbon reaction column are directed to waste.

In the illustrative apparatus, the support structure 25 includes resilient connectors 25a and 25b (including vial bushings and O-ring gaskets) provided at the lower ends of the heat exchanger and carbon reaction column. respectively, for connecting the outlets 10 and 13 to the sample vials 11 and 12. When the tray 19 is in the sealed vial position, the combustion products discharged from the lower outlet 10 of the heat exchanger flow downwardly into the sample vial 11 with the liquids being retained in the vial by gravity and the gases continuing on into the conduit 15 through a suitable discharge passageway formed in the resilient connector 25a. Likewise, a suitable passageway is provided in the connector 25b for admitting fluids to the carbon sample vial 12 from a transfer conduit 27 (from the first three-way valve), with gases continuing on into the carbon reaction column.

The tray 19 is held in the sealed vial position when the piston and link 21 are in their extreme upward position (i.e., upward piston motion having been transmitted to the tray through the clevis 22 and pin 23 arrangement). Inasmuch as the clevis 22 and pin 23 connection between the link 21 and tray 19 is offset with respect to the vertical centerline of the tray, it is necessary to provide means for maintaining the horizontal stability of the tray when it is in the sealed vial and partially lowered positions. To this end, i.e., to assure horizontal stability of the tray 19 and to assure proper vertical alignment of the vials 11 and 12 beneath the outlets 10 and 13, a coil spring 28 and guide pin 29 are interposed between the bottom of the tray and the lower support plate 24. The coil spring 28 is secured at its upper end to the underside of the tray 19, and at its lower end to the support plate 24 by means of a capscrew 30. As described below, the capscrew 30 is provided with an elongated head which serves as a stop for effecting tilting of the tray 19. The guide pin 29, also fixed at its upper end to the underside of the tray 19, extends downwardly through an opening 31 (having sides 31a and 31b) provided in the support plate 24.

When the tray 19 is disposed in an upright position, the guide pin 29 is urged by the spring 28 against the side 31a of the opening. Thus, when the tray 19 is in either the sealed vial position or the partially lowered position, the bias of the spring 28 urging the guide pin 29 against the side 31a of the opening in the support plate 24 provides assurance that the vials 11 and 12 remain properly aligned with their respective vial bushings to prevent skewing of the vials. The guide pin 29 also lends assurance that the tray will remain in a non-tilted condition with the vials 11 and 12 vertically aligned with and located beneath the outlets l0 and 13.

The tray 19 may be readily dropped from the sealed vial position to the partially lowered position by retraction of the piston and link 21 a predetermined distance (partially lowered position shown in phantom in FIG. 1). For tilting the tray 19 from its partially lowered (but upright) position to an inclined position, stop means in the form of the top of the capscrew 30 (see FIG. 2) is provided for engagement by the undersurface 32a of a member 32 located on the underside of the tray. As will be seen, the vertical line of contact between the member 32 and the capscrew 30 is laterally offset from the line of force running through the link 21 and pivot 23. Thus, upon downward retraction of the piston and link 21, the horizontally disposed tray 19 moves downwardly until the surface 32a engages the top of the capscrew 30. Further downward travel of the piston and associated link 21 (see FIG. 2) results in pivoting or tilting of the tray 19 about the clevis pin 23 by reason of cam action between the surface 32a and the capscrew 30.

Downward movement of the piston and link 21 is continued until the angle of tilt (about 30 from the horizontal as illustrated in FIG. 2) is such that the mouths of the sample receiving vials l1 and 12 are removed from beneath the outlets and 13 (and from access by fluids emerging therefrom) and are replaced by the waste receiving compartment 16 of the tray. The desired angle of tilt may be achieved by limiting downward travel of the piston (in a conventional manner), and by sizing the plate opening 31 and guide pin 29 such that the lower portion of the pin contacts the side 31b of the opening and thereby acts as a stop to prevent overtilt.

Restoration of the tray 19 to the horizontal is accomplished by moving the piston and link 21 upwardly a sufficient distance to disengage the surface 320 from the capscrew 30, whereupon the spring 28 and guide pin 29 arrangement take over to swing the tray back into the horizontal position.

For assuring that scintillator solution will be injected into the apparatus only when the sample vials are in their partially lowered position, a scintillator feed control valve 33 is mounted on the support structure 25, and a sensing mechanism 34 connected with the valve and extending below the support is provided for contacting the sample vial when in the raised position (and thereby disabling the valve until the vial is lowered).

It will thus be seen that the sample receiving and collecting mechanism of the present invention holds the sample vials in readiness to receive fluids in either of two positions, a raised, sealed position in which liquids and gases are retained in the system, and a partially lowered position in which liquids are collected but gases may be vented to the atmosphere. Yet the mechanism may be easily tilted to remove the vials from fluid access and substitute a waste receiver therefor, so that cleaning fluids may be directed to waste without contaminating the samples.

I claim as my invention:

1. A tiltable tray mechanism comprising, in combination, a fixed support member, a normally horizontally disposed tray arranged above the support member, a

piston and cylinder assembly fixedly mounted to the support member and disposed beneath the tray, the piston and cylinder assembly having its piston generally vertically disposed and extending toward the tray,

clevis and pin means for connecting the piston to the tray so that the tray is tiltable with respect to the piston out of its normally horizontal position, spring means interposed between the tray and the fixed support member for urging the tray into the normally horizontal position, the piston being operable to overcome the bias of the spring means upon retraction into its cylinder, and stop means carried by the fixed support member and laterally displaced from the vertically disposed piston, said stop means being located beneath the tray for engagement by the tray in response to retraction of the piston into its cylinder whereby such engagement causes the tray to be tilted with respect to the horizontal and against the bias of the spring means.

2. The mechanism defined in claim 1 in which a guide pin is fixed to the underside of the tray and extends through an opening provided in the fixed support member for engagement with the sides of the opening to thereby limit the extent of tilting movement of the tray.

3. The mechanism defined in claim 1 in which the stop means is a capscrew secured to the fixed support.

4. For use in a liquid sample preparation apparatus having a liquid outlet, a sample receiving mechanism comprising a fixed support member, a normally horizontally disposed tray arranged above the support member for holding a sample container beneath the liquid outlet, a piston and cylinder assembly fixedly mounted to the support member and disposed beneath the tray, the piston and cylinder assembly having its piston generally vertically disposed and extending toward the tray, clevis and pin menas for connecting the piston to the tray so that the tray is tiltable with respect to the piston out of its normally horizontal position, spring means interposed between the tray and the fixed support member for urging the tray into the normally horizontal position, the piston being operable to overcome the bias of the spring means upon retraction into its cylinder, and stop means carried by the fixed support member and laterally displaced from the vertically disposed piston, said stop means being located beneath the tray for engagement by the tray in response to retraction of the piston into its cylinder whereby such engagement causes the tray to be tilted with respect to the horizontal and against the bias of the spring means.

5. The sample receiving mechanism defined in claim 4 in which the tray has a compartment for holding a sample container and a separate compartment for receiving waste liquid from the liquid outlet of the apparatus, and the tray is positioned so that the sample container compartment is located beneath the liquid outlet when the tray is in the horizontal position, and the waste liquid compartment is located beneath the liquid outlet when the tray is in the tilted position.

6. The mechanism defined in claim 4 in which a guide pin is fixed to the underside of the tray and extends through an opening provided in the fixed support member for engagement with the sides of the opening to thereby limit the extent of tilting movement of the tray. :0: =0: 

1. A tiltable tray mechanism comprising, in combination, a fixed support member, a normally horizontally disposed tray arranged above the support member, a piston and cylinder assembly fixedly mounted to the support member and disposed beneath the tray, the piston and cylinder assembly having its piston generally vertically disposed and extending toward the tray, clevis and pin means for connecting the piston to the tray so that the tray is tiltable with respect to the piston out of its normally horizontal position, spring means interposed between the tray and the fixed support member for urging the tray into the normally horizontal position, the piston being operable to overcome the bias of the spring means upon retraction into its cylinder, and stop means carried by the fixed support member and laterally displaced from the vertically disposed piston, said stop means being located beneath the tray for engagement by the tray in response to retraction of the piston into its cylinder whereby such engagement causes the tray to be tilted with respect to the horizontal and against the bias of the spring means.
 2. The mechanism defined in claim 1 in which a guide pin is fixed to the underside of the tray and extends through an opening provided in the fixed support member for engagement with the sides of the opening to thereby limit the extent of tilting movement of the tray.
 3. The mechanism defined in claim 1 in which the stop means is a capscrew secured to the fixed support.
 4. For use in a liquid sample preparation apparatus having a liquid outlet, a sample receiving mechanism comprising a fixed support member, a normally horizontally disposed tray arranged above the support member for holding a sample container beneath the liquid outlet, a piston and cylinder assembly fixedly mounted to the support member and disposed beneath the tray, the piston and cylinder assembly having its piston generally vertically disposed and extending toward the tray, clevis and pin menas for connecting the piston to the tray so that the tray is tiltable with respect to the piston out of its normally horizontal position, spring means interposed between the tray and the fixed support member for urging the tray into the normally horizontal position, the piston being operable to overcome the bias of the spring means upon retraction into its cylinder, and stop means carried by the fixed support member and laterally displaced from the vertically disposed piston, said stop means being located beneath the tray for engagement by the tray in response to retraction of the piston into its cylinder whereby such engagement causes the tray to be tilted with respect to the horizontal and aGainst the bias of the spring means.
 5. The sample receiving mechanism defined in claim 4 in which the tray has a compartment for holding a sample container and a separate compartment for receiving waste liquid from the liquid outlet of the apparatus, and the tray is positioned so that the sample container compartment is located beneath the liquid outlet when the tray is in the horizontal position, and the waste liquid compartment is located beneath the liquid outlet when the tray is in the tilted position.
 6. The mechanism defined in claim 4 in which a guide pin is fixed to the underside of the tray and extends through an opening provided in the fixed support member for engagement with the sides of the opening to thereby limit the extent of tilting movement of the tray. 